spec(creative): add IAB CTV experience profiles for AdCP 3.2

[bokelley]

Problem

AdCP 3.2 needs to describe CTV home/menu and high-impact screen experiences without creating channel-named creative canonicals that duplicate the buyer asset contracts already represented by IAB Native and VAST.

The IAB Tech Lab CTV Ad Portfolio defines six experiences:

• Menu (including home-screen inventory)
• Pause
• Screensaver
• Overlay
• Squeezeback
• In-Scene

The final IAB signaling guidance maps Menu to IAB Native and the other five to NonLinear VAST. AdCP should preserve that mapping. CTV is a placement/rendering profile, not six new format_kind values.

Proposed 3.2 model

Add a shared ctv_ad_experience vocabulary with:

menu | pause | screensaver | overlay | squeezeback | in_scene

• native_in_feed accepts only ctv_ad_experience: "menu". The wire name remains stable for 3.x even though Menu is not literally an in-feed placement; a broader Native canonical name can be considered for 4.0.
• video_vast accepts pause, screensaver, overlay, squeezeback, and in_scene, constrained to a NonLinear VAST creative contract.
• One format option declares at most one CTV experience. A seller offering several experiences publishes sibling format options so buyers can route, validate, price, and preview each one independently.
• Do not add ctv_* canonical kinds. Linear CTV video remains ordinary video_vast/video_hosted; channel applicability stays on the product declaration.

Schema work

• Add the shared experience enum and document its IAB mapping.
• Extend video_vast with an explicit creative-type constraint (linear | nonlinear | either) that replaces the ambiguity of linear_required over time.
• Add VAST 4.3 and 4.4 to vast_version; document the IAB portfolio's VAST/SIMID requirements.
• Constrain the five video-backed CTV experiences to nonlinear and reject menu on video_vast.
• Allow menu on native_in_feed, with slots_override examples for tile and banner variants, and reject the other five experiences there.
• Document IAB OpenRTB placement/signaling and creative-attribute mappings, including motion level, remote interaction, QR extensions, and safe-area/aspect constraints where applicable.
• Keep experience-specific requirements in profiles/overrides instead of copying the base Native or VAST slot contract into six schemas.

Workflow and measurement

• get_products exposes one routable format option per offered CTV experience.
• validate_input verifies the experience/canonical pairing, VAST creative type and version, Native slots, and experience-specific dimensions/safe areas.
• preview_creative fixtures demonstrate remote navigation, motion behavior, QR presentation, and fallback rendering without implying that preview execution is buyer-supplied code.
• Define one rendered impression per experience opportunity; remote selection and QR activation are engagement/click events, not additional impressions.
• Add positive and negative compliance vectors for all six experiences.

Acceptance criteria

• All six IAB experiences are expressible in 3.2 using only native_in_feed and video_vast.
• Invalid pairings (for example Menu + VAST or Pause + Native) fail schema/semantic validation.
• NonLinear VAST constraints, VAST 4.3/4.4, SIMID, QR, motion, and OpenRTB signaling are documented and covered by vectors.
• Menu/home-screen Native includes tile and banner worked examples.
• Product discovery, manifest validation, preview, and measurement semantics are covered end to end.
• No new CTV-specific canonical format_kind is introduced.

References

• IAB Tech Lab, CTV Ad Portfolio Signaling and Implementation Guidelines
• IAB Tech Lab, VAST
• IAB Tech Lab, Native Advertising

Related: #5972